Refining of fatty oils



March 27, 1962 B. H. THURMAN 3,027,389

REFINING 0F FATTY OILS Filed June 25, 1958 zg-V445,

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ENQ/AM/N Eli/awww@ Ill-0 3,027,389 REFDJMG F FATIY DELS Beniamin H. Thurman, 60 Gramercy Park N., New York, N.Y. Filed .lune 23, 1958, Ser. No. '743,598 l1 Claims. (Cl. 260-425) My invention relates to the refining of fatty oils and more particularly to a concurrent-countercurrent process employing a centrifugal extractor.

Centrifugal extractors of recent design have a series of concentric stages rotating at high speed about a horizontal axis. These stages are formed by concentric walls spaced radially from each other to form annular spaces interconnected at 180 intervals by openings or slots. Such machines are designed for selective concurrent or countercurrent flow of two liquids with the purpose of contacting them intimately and separating the products. Such machines are characterized by small volumes, low hold-ups and high throughputs which together result in short contact times.

While these short times of contact are desirable in some pharmaceutical processes they have prevented such machines from being widely used in the refining of fatty oils except as they are used merely as centrifugal separators. If an attempt is made to effect refining of a fatty Voil by countercurrent fiow through the machine of the oil and an alkaline solution, the refining is not complete. The normal gum content of the crude oil and the soaps formed by the reaction between the alkali and the free fatty acids of the oil seem to produce tight emulsions which cannot be efficiently separated into clear well-refined oil on the one hand and low-free-oil soapstock on the other hand. For these and other reasons centrifugal multi-stage liquid-liquid extractors have not become popular in the refining of crude glyceride oils.

Conventionally such crude glyceride oils are usually refined by a continuous process in which the oil and the alkali are mixed and flow together through a hold-up or conditioning zone where the emulsion breaks or is conditioned for the subsequent separation. Even with efficient centrifugal separation, such conventional refining steps rarely produce oils containing less than 400 ppm. of soap. Such oils must be Washed with water, sometimes two or three times, to reduce the residual soap to below 30 ppm.

I have found that fatty oils can be efiiciently, thoroughly and economically processed if one uses concurrent mixing followed by countercurrent washing in a centrifugal extractor. It is an important object of the invention to provide a process and apparatus operating in accordance with these principles for purifying a fatty oil.

More specifically, it is an object of the invention to purify a crude or previously treated fatty oil by mixing therewith an alkali, advancing the constituents of the mixture concurrently and under turbulence to a lightliquid inlet of a centrifugal extractor while continuously delivering to the heavy-liquid inlet thereof an aqueous or washing medium, the mixture and the washing medium counterliowing each other within the extractor While under centrifugal stress. The washing medium extracts the soaps or other impurities from the oil in such manner as to produce an improved product. 'I'his sequence may eliminate one or more succeeding washing steps.

A further object is to combine the optimum conditions of concurrent mixing and conditioning with countercurrent extraction of the soapstock in a zone of centrifugal stress in such way as to accomplish a result superior to that possible with either concurrent mixing and separation alone or countercurrent mixing and separation in the same zone.

3,027,389 Patented Mar'. 27, 1%62 Further objects and advantages will become apparent to those skilled in the art lfrom the following description of specific embodiments of the invention.

Referring to the drawing:

FIG. l is a simplified flow diagram showing the general principles of the concufreut-countercurrent process of refining fatty oils in accordance with the invention;

FIG. 2 is a more complete flow diagram showing the concurrent-countercurrent process preceded by a concurrent-concurrent preliminary treatment and illustrating diagrammatically some of the structure of the centrifugal extractor; and

FIG. 3 is a cross-sectional View of a centrifugal extractor particularly well suited to the invention.

Referring particularly to FlG. l, proportioning pumps 10 and 11 pressure streams of oil and alkali from tanks 12 and 13 at relative volumes determined by the setting of a control device 13a. rI'he streams may be adjusted in temperature by respectively fiowing through heat exchangers 14 and 15 or these heat exchangers can be bypassed by opening valves 16 and 17 in respective bypass pipes.

The streams mix at a junction 18 and may be additionally mixed in a mixer 19 which may be equipped with rotary paddles or other means to mix the constituents under turbulent conditions. From this point the mixture may fiow through a heat exchanger 20 where it is heated or cooled to a temperature best suited to the succeeding steps, which are countercurrent as compared with the concurrent steps thus far described. The mixer 19 or the heat exchanger Ztl or both can serve as a conditioning zone which maintains the mixture for a time sufficient to condition it for the succeeding centrifugal treatment, toward which it flows through a pipe 2l.

This pipe 21 is connected to the light-liquid inlet 24 of a countercurrent centrifugal extractor 25 of the multistage type constituting a liquid-liquid contactor-separator in which two liquids can be contacted and separated while under a controlled centrifugal force. Within the centrifugal extractor 25 the oil is guided axially in a passage 26 (FIG. 2) and thence outwardly in a side passage 27 to an outerportion 2S of an extraction zone 30 formed within a housing 31.

At the same time, a pump 34 withdraws an aqueous or Wash medium from a tank 35 and pressures or controls the fiow of the resulting stream moving to the centrifugal extractor 25 through a pipe 36 connected to the heavyliquid inlet 37 of the extractor. The housing 31 of the extractor 25 is rotated at controlled speed about an axis A-A (FIGS. 1 and 2) by means of a drive 38, shown diagrammatically. Conventionally, the pipes 2l and 36 connect to passages in opposite ends of a shaft mounting the housing 3l and turning about the axis A-A, the connection being through appropriate rotary seals.

The wash medium advances from the heavy-liquid inlet 37 through a passage 40 (FiG. 2.) to an inner portion 42 of the extraction zone 30. Here it is acted upon by centrifugal force, aided if desired by the pressure of the pump 34 but in any event controlled thereby. Under such forces the wash medium advances outwardly through the stages of the extractor to the outer portion 28 of the extraction Zone. This action, aided and/or controlled by the pressure of the pumps iti and il, displaces the oil in such outer portion to flow inwardly through the stages of the extractor to the inner portion 4t2. From an exit area thereof it leaves the extractor through the light-liquid outlet passage 45 and the pipe 46 (FIG. 2) interconnected by means of a rotary seal and forming a part of the light-liqiud outlet 47 of the extractor. The nowpurified oil collects in a tank 4%.

The wash medium with the impurities picked up from p the oil is conducted inwardly from an exit karea of the ademas outer portion 2% through one or more side passages 50 and an axial passage 5l (FIG. 2) and from the heavy-liquid outlet 5E, of the extractor. it enters a pipe 53 through a suitable rotary seal and collects in a tank Passages 26, 27, do, d'5, do, 59 and :''l oi liiG. 2 are indicated by correspondingly numbered arrows in FiG. 1 to show the general iiow pattern.

The concentric stages ot the extractor are at diiterent radial positions, filling an intermediate portion of the extraction zone 30 between the inner and outer portions 4t2 and 28 thereof. As shown diagrammatically in 2, these stages are formed by and between concentric circular walls dit forming annular spaces 6i therebetween. The annular spaces are interconnected at 180 intervals by slots o2 through which the oil must liovv inwardly and the wash medium outwardly to elect a dispersion or" one in the other and produce an extensive area of contact of the two liquids. This mixing action is repeated in the slots at each radial position. At the same time, the centrifugal force in each annular space el tends to separate the dispersion formed by the adjoining slots.

The two liquids thus repeatedly mingle and separate during their countercurrent tlow through the extraction zone 30, indicated by the opposed arrows 6d and 65 of FiG. 1. ln each mixing or mingling step the predominant action is believed to be a dispersion of the wash medium into the oil, albeit some dispersion of the oil into the Wash medium may take place. The mixing in the presence ot centrifugal force tends to eiect rapid separation and prevent formation of stable emulsions.

With water as the wash medium, the rotating liquid in the extraction Zone 3th is alternately water-continuous and oil-continuous at ditierent radial positions, creating what may be considered actual interfaces in each annular space 61. Considering the entire extraction Zone 3b as a unit, there are in addition maior or principal interfaces between the oil and water in the inner and outer portions i2 and Ztl.

FlG. 2 shows essentially the equipment of FlG. 1, except for the omission of heat exchangers ld and l5, preceded by another series of continuous treating or refining steps. Proportioning pumps 7h and il meter and pressure streams of oil and alkali 'from tanks 72 and 73. Heat exchangers 7a and 75 adjust the temperature or can be bypassed as previously described. rihe streams meet and mix at a junction 7o and may be additionally mixed in a mixer 77, being adjusted in temperature in a heat exchanger 78 as previously described. The conditioned mixture is separated in any suitable way, as by a centrifuge S0, into a partially purified oil conducted to the tank 12. by a pipe iii and reaction products or soapstock conducted through the pipe 82 to storage. if no further alkali treatment is desired, the pump 1l may be shut off and the pump liti can force the oil directly to a point ahead of or beyond the heat exchanger Ztl through a pipe 83 by suitable manipulation ot' valves in the branch pipes shown.

FiG. 3 shows in somewhat greater detail some of the passages and structure of a commercial centrifugal extractor. Portions corresponding to FIGS. l and 2 are correspondingly numbered. FEiG. 3 shows also a shaft 9u and bearings 92 supporting the housing 3l. lt illustrates also a base 53 and an enclosure 9d surrounding the housing 3l. An added feature is a iiush to the outer portion 28 of the extraction zone 30, preferably to the zone or area of exit of the heavy or wash medium therefrom. lf the wash medium has extracted sulicient impurities to become viscous or too hard to ow through the passages 50, Si and 53, it may be diluted in such exit zone by a stream of water or other diluent pumped through a pipe 9o. This liquid 'liows through a radial passage 97 bypassing the extraction stages and through axial branch passages 9S formed in an annular projection 99 of generally triangular cross section disposed in the outer portion 2S of the extraction zone. The added liquid discharges into the wash medium as the latter is about to enter the passages S0, diluting same and facilitating its continuous exit from the machine.

Considering iirst the use of the invention in` the direct alkali refining of glyceride oils, attempts to effect the entire refining in the centrifugal extractor by counterllowing therethrough the crude oil and an alkali solution have not proved commercially satisfactory. rhe repeated mixing of the soap with the oil in the several stages and the over-all shortness of contact time in the machine are not conducive to goed retining of glyceride oils, particularly those crude oils containing more than 1% of free fatty acids. Essentially the same is true of attempts to mix the oil and alkali outside the machine and use the extractor merely as a centrifugal separator.

The present invention is based on a uding that glyceride oils can be adequately and economically retined by a concurrent mixing ahead of a centrifugal extractor, followed by countertlowing the mixture with water or other wash medium in the extractor to extract the soapstock from the mixture. While of some utility on all crude or degummed glyceride oils, rthe process of the invention is particularly well suited to the alkali refining of oils which are low in gums and free fatty acids. The alkali soapstocks thereof are readily picked up by the counterliowing wash medium, which never contains any large concentration of soap and has little tendency to emulsify. For example, if the oil contains only 0.1% soap by weight and if 10% water is used as the wash medium, the heavy-liquid effluent of the machine Will contain only about 1% soap. Excellent results are obtained using the process in the rening of crude nut oils, eg. coconut, palm kernel and babassu oils, or degummed vegetable oils, degummed soy bean oil, or other similar oils containing about 0.1-0.5 gums and 0.050.8% free atty acids, although the invention is not limited thereto.

In the relining of such oils by caustic, for example, a relatively strong caustic solution is preferred, typically 16-20 B. up to 30-50" B. The mixture is conditioned for separation by ilow through a coil, pipe or turbulent Zone, provided by the mixer i9 or the heat exchanger 20 or other equipment. it is then delivered to the extractor 25. While stratication tends to take place within the extractor at caustic strengths above about 20 B., the counteriiow of water or other wash medium overcomes this tendency.

The'invention is also excellently suited to the caustic re-rening of glyceride oils to remove color or other impurities which remain following a preliminary alkali refining step. For example, crude oils refined with ammonia or soda ash are quite low in free fatty acids but Otten require treatment with caustic to reduce their color to commercial values. For example, the equipment of FIG. 2 can be employed to mix a soda ash solution from the tank 73 with a crude glyceride oil from the tank 72, the mixture iiowing through the mixer 77 and the heat exchanger 73 to lthe centrifuge 30 where it is separated to recover the oil which desirably is treated with the caustic solution from the tank 13. Similar steps employing aqueous ammonia solutions as the alkali will produce a similar oil. With excesses of soda ash as low as 1.5 times the amount required to neutralize the fatty acids, a vapor separating chamber may be employed between the mixer 77 and the centrifuge 80. `In all such instances, the oil from the centrifuge may be of undesirably high color and can best be subject to the re-relining step. This is particularly true as concerns cottonseed oil but also applies to other glyceride oils which upon a preliminary refining produces an oil of undesirably high color content, of deleterious taste or odor, or having an undesirably high content of impurities removable by a strong caustic treatment.

In the re-retining step, a concentrated caustic soda solution of about 20-50" B. is Withdrawn from the tank 13 of FiG. 2 and mixed with the oil. The amount of caustic solution can be relatively small, the amount being desirably about 1/2 to 4%. The mixture can be delivered to the extractor 25 at room temperature or above. Best results are usually obtained in the range of about 120- 180 F. A supplementary stream of water or salt solution can be supplied to the extractor through the pipe 96 of FIG. 3 to aid the continuous discharge of the wash medium, but this is usually not required.

If the partially refined oil contains residual free fatty acids, the caustic from the tank will react therewith to form a small amount of soap. In addition, there may be a small degree of reaction between the alkali and the oil, producing additional small amounts of soap. In any event, the wash medium discharging from the extractor will be a dark liquid consisting largely of water containing excess caustic soda and a small amount of soap. The refined oil collecting in the tank 48 is usually of sur prisingly low soap content.

All practices of the invention heretofore suggested offer many significant advantages. By concurrently mixing and conditioning the system, optimum conditions can be selected without limitation to the time the oil is present inthe extractor or the mixing-coalescing actions therein. By then following the concurrent mixing and conditioning with a countercurrent extraction of the soapstock in a centrifugal extractor it is possible to accomplish results superior to those obtainable by use of other sequences.

By the concurrent-countercurrent sequence it is possible to extract the soapstock from the oil without emulsiiication, achieving a complete refining and good color reduction. Here and elsewhere the word soapstock is used both with reference to the product resulting from direct alkali refining and the product resulting from re-refining by use of concentrated caustic solution.

In conventional refining of glyceride oils employing centrifugal separation, the separated oil often contains about 0.04-0.3% residual soaps and must be subjected to one or two washing steps to reduce the residual soap content to the figure of 30 p.p.m. or less, as is usually requisite. This is true whether the oil results from the direct alkali refining or from re-refining by use of concentrated caustic solutions. The present invention reduces or eliminates the need for subsequent washing steps.

The invention gives a sharp separation of the oil from the soapstock and produces no stratification diiculties with strength of caustic of about 20 B. or higher.

Importantly, the process requires less water than conventional processes with their water washing steps. The problem of waste water is very acute in many oil refineries, which commonly employ -20% water in a re-refining operation and about 15% water in a water wash step. The present process employing countercurrent extraction requires only about 3-15% Water with 510% being the most common range.

Temperatures of the mixture delivered to the extractor 25 are not usually critical and may be adjusted by the exchangers 14 or 15 operating on the unmixed iniiuent materials or by the exchanger operating on the mixture. Temperatures at the point of entry into the extractor may range from about 100 F. to about 180 F. Additional heat can sometimes be supplied within the extractor as by supplying thereto a wash medium which is at a temperature higher than the incoming mixture.

Water is the preferred washing medium but may carry Various salts. The salts are often beneficial in bettering the separation. Dilute solutions of salts such as sodium carbonate, sodium sulfate, sodium bicarbonate, etc., and salts of organic acids are useful.

As an example of a direct alkali refining, the invention can be employed under approximately the following conditions to give good results on a crude soy bean oil containing about 0.5% free fatty acids and about 0.4% gums (phosphorus content times 26). About 1.5% by weight of a 20 B. caustic solution, being an amount 3 times that corresponding to the free fatty acids, is mixed with 6 the oil at room temperature and heated to a temperature of about 160 F. in the exchanger 20. About 7.5% of water, based on the weight of the mixture, can be fed to the heavy-liquid inlet 37 at a temperature of about 160 F. The residual soap in the eiiiuent oil will commonly be less than 100 ppm. under these conditions.

As an example of re-refining cottonseed oil originally containing 1.5% free fatty acids and 1.6% gums after centrifugally separating the soapstock. resulting from mixing 4.0% of a 15% concentration of soda ash solution therewith, the following conditions will be found beneficial. About 2% of 26 B. caustic can be mixed with the oil in the mixer 19 equipped with rotating paddles, the mixture being heated to a temperature of about 150" F. before entering the extractor. About 10% of tap Water, used as a wash medium, counter-flows the oil in the extractor 30. The resulting purified oil discharging into the tank 48 contains less: than 50 pp m. residual soaps and a bleach 0.3R lower than the cup bleach.

The invention is well suited also to the alkali treatment of oils in the miscella. Thus oils containing up to 50% of oil solvents such as hexane, heptane or trichloroethylene can be refined or re-refined by the concurrentcountercurrent steps outlined herein. The oil solvent can be separated from the oil leaving the light-liquid outlet 47 of the extractor, this separator being by conventional methods. In this and other variations the pressures throughout the extractor can be maintained super-amospheric without difficulty thus making it possible to prevent liberation of solvent in vapor form in the extraction step. Operation of the process in the miscella stage makes it possible to improve the operation of the invention on oils of high gum and fatty acid contents. Refining or re-rening of cottonseed or soya oils of common gum and free fatty acid contents is improved if operation is in the miscella throughout.

The exemplified processes will suggest other variants to those skilled in the art, as will also the arrangements of apparatus illustrated. In this latter connection the oil from the equipment 70-81 of FIG. 2 can sometimes with advantage be delivered directly to the extractor 30 where it can be counterflowed with a. wash medium. In other instances, some water or other wash medium can be supplied to the oil from the tank 13, additional wash medium being counterfiowed in the extractor 30.

I claim as my invention:

1. A concurrent-countercurrent process for refining fatty oils, which process includes the steps of: mixing a low-gum, low-free-fatty-acid oil with an alkaline reagent capable of combining with impurities of the oil; pumping the resulting mixture before any centrifugal separation thereof through an elongated conditioning zone under turbulence and then into the outer portion of a Zone of centrifugal separation rotating about a horizontal axis and sealed from the atmosphere except for exit passages; fiowing into an inner portion of said zone of centrifugal separation at a position much closer to the axis of rotation than the position at which the conditioned mixture enters said zone a stream of Wash medium substantially immiscible with the oil; counterflowing the materials of said streams in said zone between said positions while rotating said zone about said horizontal axis and whilel repeatedly mixing and separating the wash medium and the mixture in different radial zones between said positions, said wash medium extracting the combined impurities from the oil; and continuously removing from said zone through one of said exit passages during said rotation a stream of purified oil from which said impurities have been largely removed and through another of said exit passages a stream of the wash medium carrying the extracted combined impurities.

2. A process as defined in claim 1 including the step of subdividing said wash medium and dispersing same in the oil a plurality of times during the liow of the spense@ 7 wash medium through said radial zones away from said inner portion.

3. A concurrent-countercurrent process for refining fatty oils, which process includes the steps of: rotating about a horizontal axis an extraction zone to establish a high centrifugal force therein, said zone having inner and outer positions at different radial distances from said axis; mixing a, low-gum, low-free-fatty-acid oil with au alkaline reagent; conditioning the mixture before subjection to said centrifugal force by flowing same under turbulence through an elongated conditioning zone ahead of said extraction zone; flowing the resulting conditioned mixture as a stream to said outer position of said extraction zone during rotation thereof about said axis under sufcient pressure to move the oil of the mixture inwardly past said inner position to an oil exit area even closer to said axis; counter-owing an aqueous material and the oil of said stream in an intermediate portion of said extraction zone between said inner and outer positions during said rotation by flowing said aqueous material from said inner position to an outer exit area of said extraction zone outwardly beyond said outer position while the material of said oil stream ows inward from said outer position of said extraction zone toward said oil exit area, said extraction zone exiting to the atmosphere exclusively through passages respectively communicating inwardly with said outer exit area and said oil exit area, said pressure maintaining a superatmospheric pressure throughout said extraction zone; and withdrawing respectively and continuously from said oil exit area and said outer exit area through said passages during such rotation a stream of oil from which materials have been extracted by said aqueous material and a stream of aqueous material containing extracted material.

4. A process as defined in claim 3 including the steps of repeatedly subdividing and separating said aqueous material and the oil of said stream at different radial positions during low of said aqueous material outwardly from said inner position through said intermediate portion to said outer position.

5. A process as defined in claim 3 in which said alkaline reagent is a strong caustic solution of about 16 B. to about 50 B.

6. A process as deiined in claim 3 in which said oil is a partially reiined oil produced by mixing an alkali with a glyceride oil containing free fatty acids and gums to react therewith and produce soapstock therein, and separating said soapstock to produce said oil with which said alkaline reagent is mixed.

7. A process as defined in claim 6 in which the oil resulting from the separation of said soapstock contains color impurities, and in which said alkaline reagent is a caustic solution of about 20 B. up to about 50 B.

8. A concurrent-countercurrent process for reining fatty oils, which process includes the steps of: continuously mixing under pressure proportioned streams of a fatty oil containing about 0.l-0.5% gums and about 0.05-0.8% free fatty acids and an amount of alkali solution in excess of that amount theoretically required to react said fatty acids thus forming soapstock in the oil, said soapstock including at least apart of said gums; conditioning the resulting mixture by owing same under Vpressure and turbulence through a stationary elongated zone; delivering the conditioned mixture to a zone of centrifugal separation sealed from the atmosphere and exiting thereto exclusively through passages connected to said zone of centrifugal separation, said conditioned mixture being delivered to said Zone of centrifugal separation at an outer position thereof while rotating such zone about a horizontal axis; largely separating said soapstock of said mixture by centrifugal force near said outer position and moving the thus separated soapstock outwardly beyond such position to an outer exit area of said zone of centrifugal separation; applying sutlicient pressure to said mixture delivered to said zone of centrifugal separation to force the separated oil of said mixture with a residual soapstock content inward toward said axis past an inner position of such zone to an inner exit area of such zone close to said axis; pumping into said zone of centrifugal separation at said inner position about 3-l5% of an aqueous medium while such Zone is rotating at such speed as to move such aqueous medium outward by centrifugal force to counterilow said separated oil between said positions and to iiow thence to said outer exit area; repeatedly intermingling and separating the inward iowing separated oil and the outward tiowing aqueous rnedium between said inner and outer positions; continuously withdrawing from said outer exit area through one of said passages soapstock diluted by said washing medium; and continuously withdrawing from said inner exit area through another of said passages oil washed by said aqueous medium containing less than ppm. of soap.

9. A process as dened in claim 8 in which the temperature of said resulting mixture at the time of delivery to said zone of centrifugal separation is about 100- F.

10. A process as dened in claim 8 in which said alkali is a caustic alkali solution of about 16-50 B.

11. A process for retining fatty oils containing free fatty acids and gums, which process includes the steps of continuously mixing with said fattyV oil sutlicient nonsaponifying alkali to react with at least a part of the tree fatty acids to form foots containing soaps and gums; separating said foots; continuously mixing with the separated oil about 1/2 to 4% of caustic soda solution of about 20-50" B.; conditioning the resulting mixture for separation by owing same under pressure and turbulence through an elongated zone; delivering the conditioned mixture-to a zone of centrifugal separation at an outer position of said zone while rotating said zone about an axis, said zone exiting to the atmosphere exclusively through passages connected to said zone; largely separating the heavier component of such conditioned mixture by centrifugal force near said outer position and moving same outwardly beyond such position to an outer exit area of said zone of centrifugal separation; applying sufticient pressure to said resulting mixture entering said zone of centrifugal separation to force the oil portion of such mixture inward toward said axis past an inner position to an inner exit area of said zone close to said axis; pumping into said zone of centrifugal separation at said inner position about 3-15% water while said zone is rotating at such speed as to move said water outward by centrifugal force to counterflow said oil portion of said mixture between said positions and to ow thence to said outer exit area; repeatedly intermingling the inward owing oil portion of said mixture and the outward fiowing water between said inner and outer positions; continuously withdrawing from said outer exit area through one of said passages the heavier component of such mixture diluted Vby said water; and continuously withdrawing from said inner exit area through another of said passages oil washed by said water,

References Cited in the file of this patent UNlTED STATES FATENTS 

1. A CONCURRENT-COUNTERCURRENT PROCESS FOR REFINING FATTY OILS, WHICH PROCESS INCLUDES THE STEPS OF: MIXING A LOW-GUN, LOW-FREE-FATTY-ACID WITH AN ALKALINE REAGENT CAPABLE OF COMBINING WITH IMPURITIES OF THE OIL; PUMPING THE RESULTING MIXTURE BEFORE ANY CENTRIFUGAL SEPARATION THEREOF THROUGH AN ELONGATED CONDITONING ZONE UNDER TURBULENCE AND THEN INTO THE OUTER PORTION OF A ZONE UNDER CENTRIFUGAL SEPARATION ROTATING ABOUT ABOUT A HORIZONTAL AXIS AND SEALED FROM THE ATMOSPHERE EXCEPT FOR EXIT PASSAGES; FLOWING INTO AN INNER PORTION OF SAID ZONE OF CENTRIFUGAL SEPARATION AT A POSITION MUCH CLOSER TO THE AXIS OF ROTATION THAN THE POSITION AT WHICH THECONDITIONED MIXTURE ENTERS SAID ZONE A STREAM OF WASH MEDIUM SUBSTANTIALLY IMMISCIBLE WITH THE OIL; COUNTERFLOWING THE MATERIALS OF SAID STREAMS IN SAID ZONE BETWEEN SAID POSITIONS WHILE ROTATING SAID ZONE ABOUT SAID HORIZONTAL AXIS AND WHILE REPEATEDLY MIXING AND SEPARATING THE WASH MEDIUM AND THE MIXTURE IN DIFFERENT RADIAL ZONES BETWEEN SAID POSITIONS, SAID WASH MEDIUM EXTRACTING THE COMBINED IMPURITIES FROM THE OIL; AND CONTINUOUSLY REMOVING FROM SAID ZONE THROUGH ONE OF SAID EXIT PASSAGES DURING SAID ROTATION A STREAM OF PURIFIED OIL FRM WHICH SAID IMPURITIES HAVE BEEN LARGELY REMOVED AND THROUGH ANOTHER OF SAID EXIT PASSAGES A STREAM OF THE WASH MEDIUM CARRYING THE EXTRACTED COMBINED IMPURITIES. 